A major difficulty in the treatment of human leukemia and other forms of cancer is the prevention of recurrence. A model system has been developed to analyze the role of the immune response in the regulation of dormant leukemia. The model system is one in which a virus induced murine leukemia has spontaneously regressed. After a period of apparent recovery, the disease recurs in a significant proportion of mice in which the disease has been regressed. The immune system provides the primary host function involved in establishing the regressed state. The focus of these studies will be to prevent leukemia recurrence by stimulation of immune response against antigens which appear during recurrent leukemia. Immunological reactivity against antigens of primary and recurrent leukemia cells and virus will be compared and then correlated to maintenance of long term regression or promotion of recurrence. Target antigens of leukemia cells and virus will be compared and then correlated to maintenance of long term regression or promotion of recurrence. Target antigens of leukemia cells will be identified and compared by immunological and immunochemical methods with the aid of immunoselected virus induced tumor cell lines. Active specific and passive specific immunization and non-specific immunostimulation during periods of leukemia dormancy will be used to prevent redevelopment of leukemia. These studies will provide useful information about immunological mechanisms by which tumor cells survive for long periods of time and then re-emerge to express their malignant potential. Such information is central to the control of recurrent neoplasia.